Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 240032 AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 732 PM EST TUE DEC 23 2014 .SYNOPSIS... A WEAK AREA OF LOW PRESSURE DISSIPATES TO THE SOUTH AND EAST OF LONG ISLAND TONIGHT. A STRONGER STORM SYSTEM WILL IMPACT THE REGION CHRISTMAS EVE THROUGH CHRISTMAS MORNING. A COLD FRONT WILL MOVE ACROSS THE REGION CHRISTMAS MORNING. HIGH PRESSURE BUILDS TO THE SOUTH THURSDAY NIGHT THROUGH SATURDAY...FOLLOWED BY A COLD FRONT EARLY SUN. LOW PRES MAY THEN IMPACT THE AREA ON MON...FOLLOWED BY SEASONALLY COLD WEATHER THRU THE MIDDLE OF THE WEEK. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... RIDGING BUILDS ALONG THE EAST COAST INTO TONIGHT AS UPPER TROUGH DIGS DEEP INTO TEXAS. AT THE SURFACE...A WEAKENING SURFACE LOW WILL DISSIPATE AS IT TRACKS JUST SE OF THE REGION TONIGHT. FORCING WILL BE LIMITED LATE TODAY INTO TONIGHT...BUT WEAK ONSHORE FLOW AND LOW LEVEL SATURATION SHOULD LEND TO MAINLY DRIZZLE AND PATCHY FOG TONIGHT. DENSE FOG POTENTIAL LOOKS LOW AT THIS POINT WITH DEWPOINTS HOLDING IN THE LOWER 40S. INCREASING POTENTIAL FOR RAIN TO DEVELOP FROM SW TO NE LATE TONIGHT AS FORCING WITH NEXT SYSTEM APPROACHES. TEMPS WILL REMAIN FAIRLY STEADY OVERNIGHT...GENERALLY 15 TO 20 DEGREES ABOVE SEASONABLE...IN THE 40S. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY/... MODELS IN GOOD AGREEMENT WITH DEEP UPPER TROUGH OVER THE CENTRAL US WED MORNING SLIDING TOWARDS THE EAST COAST THROUGH THU MORNING...AND THEN ACROSS THE REGION ON CHRISTMAS DAY. ASSOCIATED SURFACE LOW PRESSURE WILL MAINTAIN A TRACK VERY CLOSE TO THE CLOSED UPPER LOW WITHIN THE TROUGH...TRACKING FROM THE MID MISSISSIPPI RIVER VALLEY WED MORNING AND NE THROUGH THE GREAT LAKES INTO ONTARIO/W QUEBEC WED NIGHT INTO CHRISTMAS. AHEAD OF THIS SYSTEM...A DEEP SW FLOW WILL HAVE A SUBTROPICAL MOISTURE FEED (PRECIPITABLE WATERS OF 4 TO 5 STDS ABOVE NORMAL)INTO THE REGION DURING THIS PERIOD. INCREASING LIFT VIA A DEVELOPING 60-70 KT LLJ OVER A WARM FRONT WILL HAVE THE CHANCES FOR MODERATE RAIN INCREASING LATE TONIGHT INTO EARLY WED MORNING ACROSS THE REGION. MODELS INDICATING THAT WARM FRONT MOVES NORTH OF THE REGION LATE WED...WHICH SHOULD ALLOW A TRANSITION TO CONVECTIVE SHOWER ACTIVITY FOR LATE WED INTO WED NIGHT WITH MODERATE TO HEAVY RAIN SHOWERS. POTENTIAL FOR DENSE FOG DEVELOPMENT WED AFT/EVE IN WAKE OF WARM FRONT AS TDS JUMP INTO THE 50S...WITH LIMITING FACTOR THE STRONG LOW-LEVEL WINDS. POTENTIAL FOR ISOLATED TSTM ACTIVITY LATE WED INTO WED NIGHT WITH MARGINAL ELEVATED INSTABILITY AND STRONG FORCING AS WELL...WHICH MAY CULMINATE IN A FINE LINE OF LOW-TOPPED CONVECTION LATE WED NIGHT/EARLY THU MORNING AHEAD OF APPROACHING STRONG COLD FRONT/SHORTWAVE ENERGY. MESOSCALE MODELS DEPICTING HIGHER THREAT MAY BE ACROSS LI AND SE CT WITH STRONGER LLJ AND INSTABILITY. BIGGEST THREAT WITH ANY CONVECTIVE LINE WOULD BE LOCALIZED DAMAGING WIND GUSTS WITH ANY CONVECTION MIXING DOWN A GREATER PERCENTAGE OF THE 50-60 KT 950MB LLJ. THIS CONVECTIVE POTENTIAL COMBINED WITH ANOMALOUSLY MOIST ENVIRONMENT DOES PRESENT POTENTIAL FOR HYDRO IMPACTS...SEE HYDROLOGY SECTION. OUTSIDE OF CONVECTION...WINDS INCREASE WITH THIS SYSTEM LATE WED/WED EVE IN WAKE OF WARM FRONT. ALTHOUGH 950 HPA WINDS INCREASE TO 50 TO 60 KT WED NIGHT...LIMITED MIXING SHOULD KEEP SOUTHERLY WINDS TO 15 TO 25 MPH WITH GUSTS 30 TO 35 MPH. STRONGEST WINDS COAST AND HIGHER ELEVATIONS...WITH ISOLATED 40 MPH GUSTS POSSIBLE WED NIGHT. STRONGEST SYNOPTIC WINDS WILL LIKELY BE BEHIND COLD FRONTAL PASSAGE THU MORNING INTO AFTERNOON AT 20 TO 25 MPH WITH GUSTS UP TO 40 MPH WITH DEEP MIXING AND MORE FAVORABLE MOMENTUM TRANSFER IN WAKE OF SHORTWAVE. THE THREAT FOR WIND ADVISORY GUSTS IS LOW. RAIN GRADUALLY TAPERS OFF FROM WEST TO EAST CHRISTMAS MORNING AS COLD FRONT MOVES ACROSS THE REGION. TEMPS WILL RUN WELL ABOVE SEASONABLE...GENERALLY RANGING FROM THE 40S AT NIGHT TO THE 50S DURING THE DAY. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... HIGH PRES RIDGE SLIPS E OF THE CWA THRU SAT...ALLOWING FOR INCREASING SWLY FLOW. TEMPS ALOFT 5-7C AT H85...SO HIGHS WILL BE ABV NORMAL FRI AND SAT. MRNG TEMPS MAINLY ABV NORMAL...EXCEPT CLOSE TO NORMAL OUTLYING SPOTS DUE TO GOOD RADIATIONAL COOLING. DRY THRU THE PERIOD. MOISTURE STARVED CDFNT PASSES SAT NGT. THEREAFTER...MAJOR DIFFERENCES IN THE MODEL PROGS. THE GFS ALLOWS COLD AIR TO CONTINUE TO INFILTRATE THE CWA SUN...WHEREAS THE ECMWF STALLS THE FRONT OVER THE REGION HALTING ANY CAA. ON MON...THE ECMWF BRINGS LOW PRES RIGHT THRU THE CWA RESULTING IN A RAINY DAY WITH PERHAPS A LITTLE FZRA INTERIOR IN THE MRNG. THE GFS KEEPS WEAK LOW PRES S OF THE REGION AND NO PCPN WITH MUCH COLDER TEMPS. ON TUE AND WED THE SOLNS ALIGN AGAIN AND HIGH PRES BUILDS IN ALONG WITH SOME ARCTIC AIR. MAYBE SOME FLURRIES. FOR NOW...THE ECMWF FOR SUN AND MON APPEARS TO BE AN OUTLIER BASED ON THE GFS...GFS ENSEMBLES AND 00Z ECMWF. THE FCST THEREFORE IS HEDGED MILDER ON SUN...AND COLDER MON WITH INCREASED SNOW CHCS...SIMILAR TO THE 00Z ECMWF SUGGESTION. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... ***HIGH IMPACT EVENT WEDNESDAY/WEDNESDAY NIGHT*** WEAK LOW PRESSURE ALONG A WARM FRONT JUST SOUTH OF LONG ISLAND THIS EVENING. THE LOW WILL TRACK NE OVERNIGHT WHILE WEAKENING AND EVENTUALLY DISSIPATE WED MORNING. MEANWHILE...ANOTHER WARM FRONT ASSOCIATED WITH A STRONGER AREA OF LOW PRES APPROACHING FROM THE W...WILL LIFT THROUGH THE AREA WED AFTN. IFR/LIFR WITH LOCALLY VLIFR CONDS POSSIBLE AT TIMES THROUGH WED MORNING. THINKING THAT ONCE THE RAIN MOVES IN AROUND 12Z WED...CONDS...ESPECIALLY VSBY...WILL IMPROVE SLIGHTLY. PERIODS OF MODERATE TO HEAVY RAIN EXPECTED THROUGH THE DAY WITH 50-60KT LLJ AND LLWS DEVELOPING. SOME UNCERTAINTY IN TIMING OF WARM FROPA IN THE AFTN BUT IT APPEARS TO BE SOMEWHERE BETWEEN 17Z AND 21Z WITH LIGHT WINDS (LESS THAN 10 KT) SHIFTING FROM ELY TO SLY AND INCREASING. COULD HAVE GUSTS IN THE 20S AT COASTAL TERMINALS AS WINDS OFF THE DECK WILL BE INCREASING. HOWEVER...STRENGTH OF SFC INVERSION WILL DETERMINE HOW MUCH...IF ANY...WILL MIX TO THE SFC. .OUTLOOK FOR 00Z THURSDAY THROUGH SUNDAY... .WED NIGHT...IFR IN RA. CHC +RA AND A FEW TSTMS. S 15-20G20-25KT. .THU...IMPROVING TO VFR IN THE MORNING. WINDS SHIFT W EARLY 20G30-35KT. CHANCE OCCASIONAL GUSTS 35-40KT. .THU NIGHT...VFR. W 15-20G30-35KT EVE...DIM 10KT. .FRI...VFR. .SAT...VFR. .SUN...VFR...WITH CHANCE OF SUB VFR LATE IN THE DAY. && .MARINE... SEAS ON THE OCEAN WILL RANGE FROM 6-9 FT TODAY AND TONIGHT. WINDS CONTINUE TO SUBSIDE THIS AFTERNOON INTO EVENING...BUT SCA OCEAN SEAS WILL REMAIN SMALL CRAFT ADVISORY THROUGH TONIGHT. BY WEDNESDAY AFTERNOON...SCA LEVEL WIND GUSTS WILL DEVELOP ON ALL WATERS ALONG WITH OCEAN SEAS BUILDING TO 5-7 FT AS LOW PRES MOVES NORTH THROUGH THE WATERS. A COLD FRONT PUSHES ACROSS THE WATERS THURSDAY MORNING. GRADIENT TIGHTENS...AND GALE FORCE WINDS GUSTS POSSIBLE ON ALL WATERS THURSDAY AFT INTO EVE. THEN WINDS AND SEAS WILL STEADILY IMPROVE THU NGT...WITH SCA COND ENDING ON THE OCEAN BY MID MRNG FRI. WINDS AND SEAS WILL THEN REMAIN MAINLY BLW SCA LVLS THRU MON...ALTHOUGH ON THE ERN OCEAN 5 FT SEAS MAY DEVELOP SAT INTO SAT NGT. && .HYDROLOGY... AN ADDITIONAL 1 1/2 TO 2 INCHES OF RAIN WITH LOCALLY HIGHER AMOUNTS WEDNESDAY THROUGH EARLY THURSDAY MORNING WITH MINOR URBAN AND POOR DRAINAGE FLOODING LIKELY. MINOR SMALL STREAM FLOODING IS POSSIBLE FOR A FEW OF THE FLASHIER SMALL RIVERS/STREAMS IN NE NJ/LOWER HUDSON VALLEY/AND SW CT...IF HIGHER RAINFALL AMOUNTS ARE REALIZED. WITH CONVECTIVE POTENTIAL WED NIGHT...AND 1 HR FFG OF 3/4 TO ONE INCH IN THIS AREA...THERE IS A LOW PROBABILITY OF FLASH/AREAL FLOODING. NO SIGNIFICANT PCPN FRI-SUN. LOW PRES MAY IMPACT THE HSA MON...BUT THE TRACK AND INTENSITY IS TOO UNCERTAIN TO DETERMINE HOW MUCH IF ANY PCPN WILL FALL. && .TIDES/COASTAL FLOODING... LOCALIZED MINOR COASTAL FLOODING POSSIBLE ACROSS MAINLY THE SOUTH SHORE BAYS OF LI AND NYC WITH WED MORNING HIGH TIDE. THREAT IS SLIGHT FOR LI WESTERN SOUND. ONLY A LOW POTENTIAL FOR LOCALIZED MINOR FLOODING WITH WED NIGHT HIGH TIDE WITH STRONG SOUTHERLY WINDS...AS 2 TO 2 1/2 FT SURGE NEEDED FOR MINOR FLOODING. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. NJ...NONE. MARINE...SMALL CRAFT ADVISORY FROM 4 PM WEDNESDAY TO 6 AM EST THURSDAY FOR ANZ330-335-338-340-345. SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ350-353- 355. && $$

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